An exhaust aftertreatment system associated with an engine may include a reductant supply system for delivery of a reductant fluid into an exhaust stream of the engine. The reductant supply system may include a reductant fluid tank for storing the reductant fluid, fluid conduits for transporting the reductant fluid throughout the reductant supply system, a pump for propelling the fluid throughout the reductant supply system and an injector that delivers the reductant fluid into the exhaust stream of the engine. Additionally, one such fluid conduit may be a recycle line that returns some of the reductant fluid being transported throughout the reductant supply system to the reductant fluid tank.
Customarily, the flowrate of reductant returning to the reductant fluid tank is controlled by placing a restriction, such as a throttle-valve, in the recycle line. Because the cross-sectional area of this restriction is constant, the flowrate of the reductant fluid sent to the injector is therefore a function of pump speed. However, if the pump is undersized relative to the flowrate needed at the injector, it may fail to meet the demand required at the injector. Therefore, reductant supply system designers typically specify a pump that is oversized relative to the maximum flowrate required by the injector, with some excess energy being lost as heat during passage of the reductant fluid through the supply system, including the restriction. Such designs, therefore, are energy inefficient.
One reductant supply system design is described in the Patent Cooperation Treaty application PCT/EP2013/050783 having publication number WO/2013/135401 (the '401 publication). The '401 publication describes a reductant supply system that may include a reductant fluid tank for storing the reductant fluid, fluid conduits for propelling the fluid throughout the reductant supply system, a pump for propelling the fluid throughout the reductant supply system and an injector that delivers the reductant fluid into an exhaust stream. The '401 publication also describes that it may include a recycle line.
Importantly however, the '401 publication describes that the restriction in the recycle line is replaced by a proportioning valve. Further, the '401 publication describes that the proportioning-valve includes an orifice with a variable cross-sectional area, and the period the orifice is open is variable too. Accordingly, the flowrate of the fluid sent to the injector is a function of the pump speed, the cross-sectional area of the orifice and the period the orifice is open, thereby leading to complex closed loop control schemes since pump speed, cross-sectional area of the orifice and duration the orifice is open all control the flowrate of fluid sent to the injector.
Hence, more energy efficient reductant supply systems without the need to employ complex closed loop control schemes are necessary. The present disclosure is directed to overcoming one or more problems set forth above and/or other problems associated with the prior art.